Torque motor-driven spool valves are well known in the art including such valves which operate through the utilization of a rotary torque motor having a drive member extending from the rotor thereof into contact with the spool valve to directly reciprocate the spool valve within a bore provided in the valve housing to thereby control the flow of fluid from a source thereof to the load in response to electrical signals applied to the drive motor. Typical of such direct drive servovalves is that illustrated in U.S. Pat. No. 4,793,377 issued Dec. 27, 1988, to Larry E. Haynes et al. The invention described and claimed herein is an improvement over the direct drive servovalve disclosed in U.S. Pat. No. 4,793,377 and therefore the disclosure of U.S. Pat. No. 4,793,377 is incorporated herein by this reference.
Other prior art known to applicants are U.S. Pat. No. Re. 16,026; U.S. Pat. Nos. 343,416; 2,912,870; 4,081,172; 4,126,296; 4,339,737; 4,384,703; 4,480,813; 4,614,812; 4,813,455; as well as Autrian Patent No. 1922 issued Feb. 1, 1900, and Norwegian Patent 42,506 issued Feb. 22, 1926.
It is critical in direct drive servovalves that the rotational movement of the drive member of the drive motor be limited. Such limitation is necessary during energization of the motor to absorb the full stroke rotor inertia without part damage or deformation. In prior-art valves, it has been traditional to provide such limitation by pins or similar stops keyed to or inserted into the rotor casing to be engaged by a protrusion from the rotary drive member. Alternatively, such limitation has been provided by pins or similar members extending through or from the rotary to engage stop surfaces provided in retainer plates or the rotor or stator housings.